Not all blockchains are created the same. However, there are many characteristics that most blockchains today share. The best way to get an idea of these blockchain fundamentals before jumping into Ethereum is to take a look at how the Bitcoin Blockchain works.
Chapter 7. The Blockchain - Andreas Antonopoulos, Mastering Bitcoin, 2015 [20 min read]
This chapter from Andreas Antonopoulos's textbook, Mastering Bitcoin, puts together the concepts we've learned so far and shows how these cryptographic primitives are put together in interesting data structures to create what we know as a blockchain.
Ethereum Whitepaper: Introduction to Bitcoin and Existing Concepts - Ethereum Wiki, 2015 [20 min read]
This introductory section from the Ethereum Whitepaper explains the basis of the Bitcoin blockchain, framing it as a state transition machine albeit with limited functionality. Understanding this will allow us to set up the mental model needed to understand Ethereum and its state transition system.